Pancreas Disease (PD) is a serious disease affecting Atlantic salmon (Salmon salar L). The disease causes lesions in the pancreas, including loss of pancreatic exocrine tissue and fibrosis, cardiac and skeletal muscle myopathies. It is believed that other salmonoid species, such as rainbow trout, wild Atlantic salmon, could also be infected by PD.
Outbreaks of PD were first described in 1984 by Munro et al, in Helgoland Meeresuntersuchungen 37:571-586 (1984), but PD was recognised as early as 1976. PD has also been reported in all of the major salmon farming countries of the world, including Norway, Ireland, France, Spain and Western U.S.A. (see Kent et al, Bull. Eur. Ass. Fish Path. 7:29-31 (1987); Poppe et al, in Bull. Eur. Ass. Fish Path. 9(4):83-85 (1989); and Raynard et al in Proceedings of a European Commission Workshop, Scottish Office Aquaculture Report No 1, p2-4 (1992)).
PD is known to affect fish in their first year in salt water and to spread rapidly in farmed fish held in sea cages. Ferguson et al (in Journal of Fish Diseases 9:95-98 (1986)) reported that affected fish were thin, anorexic and lethargic with a tendency to congregate in cage corners and to fail to maintain a horizontal position. In addition to the primary pancreatic lesions, Ferguson et al supra reported that fish affected by PD exhibited severe degenerative cardiomyopathy. These observations were confirmed in a later study by Murphy et al (see Journal of Fish Disease 15:401-408 (1992)) who found that cardiac and skeletal myopathy is exacerbated in fish infected with PD.
In Ireland over the period 1988-1992 PD resulted in 15-20% of recorded mortalities in salmon smolts in their first year at sea. The estimated cost to the Irish industry in terms of loss of production is currently thought to be around .English Pound.25 million per year. The current 1994 production figures for Norway, Scotland and Ireland are as follows:
______________________________________ Tonnes of salmon Numbers of smolts put Country produced to sea ______________________________________ Norway 200,000 80 million Scotland 55,000 20 million Ireland 44,000 7 million ______________________________________
McVicar et al postulated that PD was caused by an infectious agent. This proposition is supported by the results of epidemiological studies and transmission experiments by various workers, which suggest an infectious aetiology for the disease, (see McVicar in Aquaculture 67:71-78 (1987); McVicar in Bull. Eur. Ass. Fish Path. 10:84-87 (1990); Raynard et al, Dis. Aquat. Org. 15:123-128 (1993)); and Murphy et al (1992) supra). Recently Houghton (1994) 18: 109-118 reported that fish become resistant to re-infection after inoculation with PD, supporting the notion that PD is caused by an infectious agent. However, to date no infectious agent has been isolated despite numerous attempts to do so (see McVicar (1987) supra; Munro supra; and Murphy supra).